1. Field of the Invention
The present invention relates to electron-beam processed films for microelectronics structures, such as integrated circuits (xe2x80x9cICxe2x80x9d). More particularly, this invention relates to an improvement in the method of processing such films which results in uniform, dense films, some of which also possess a low dielectric constant and a low wet etch rate.
2. Background of the Invention
Various devices, such as multichip modules, printed circuit boards, high-speed logic devices, flat panel displays, integrated circuits and other microelectronics devices, require deposited or spun-on dielectric films.
One commonly used technique to produce such a desirable film onto a substrate involves thermal anneal or thermal cure at a temperature range between 350xc2x0 C. and 900xc2x0 C. for about 1 hour. See xe2x80x9cSpin/Bake/Cure Procedure for Spin-On-Glass Materials for Interlevel and Intermetal Dielectric Planarizationxe2x80x9d brochure by AlliedSignal Inc. (1994)(thermally cured spun-on films) and Kern, W., xe2x80x9cDeposited Dielectrics for VLSI,xe2x80x9d8(7) Semiconductor International 122 (July 1985)[xe2x80x9cKernxe2x80x9d]; Gorczyca, T. B., et al., xe2x80x9cPECVD of Dielectrics,xe2x80x9d8(4) VLSI Electronics Microstructure Science (New York 1984)[xe2x80x9cGorczycaxe2x80x9d]; and Mattson, B., xe2x80x9cCVD Films for Interlayer Dielectrics,xe2x80x9d Solid State Technology 60 (January 1980)[xe2x80x9cMattisonxe2x80x9d](thermally annealed chemical vapor deposited (xe2x80x9cCVDxe2x80x9d) films). However, several disadvantages are associated with thermal processing.
In applications wherein a spin-on glass film (xe2x80x9cSOGxe2x80x9d) is spun onto a substrate, siloxane-type SOGs are susceptible to damage by oxygen plasmas. During subsequent IC processing, SOGs which have been damaged by oxygen plasma are prone to outgassing of moisture, which often leads to electrical and mechanical reliability failures. In addition, the thermally cured SOGs"" instability to oxygen plasma also contributes not only to manufacturing difficulties such as delamination, but also to physical, mechanical and cosmetic deficiencies in the final product such as increased porosity, increased shrinkage, and poor planarization.
Second, the use of such high temperatures for curing silicate SOGs also causes the oxidation and degradation of silicides. This often leads to device failures caused by silicide degradation or degradation of the shallow dopant profiles in advanced ICs. Further, the presence of this oxidized surface layer disadvantageously affects the overall electrical performances of the IC by increasing the resistance or removing the electrical contact to silicides as well as by contributing to degradation of interconnections between transistors.
In applications wherein the substrate is coated with a CVD film, an additional annealing step at high temperatures up to about 1000xc2x0 C. is also required in order to improve the quality of the CVD film. However, this leads to complications and device failure problems such as silicide degradation, hot carrier degradation, device instabilities, and the like. Though these difficulties are similar to those observed with thermal processing, the magnitude of the effects is greater because the temperatures involved are significantly higher.
In growing ultra-thin gate oxides and nitrides on substrates, one known problem is the inability to control the uniformity of their growth. Prior art methods for growing such oxides employ single wafer Rapid Thermal Processing systems (xe2x80x9cRTPxe2x80x9d) or furnaces as described in, for example, Sheets, R., xe2x80x9cRapid Thermal Processing Systems,xe2x80x9d Microelectronic Mfg. and Test, 16 (July 1985). However, growth failure will occur in these methods if contaminants are present at amounts as low as parts per billion. This inability to produce such uniform oxides and nitrides often leads to subsequent burning of the oxide or nitride during operation of the IC and thus affects its overall reliability.
It is desirable for all advanced ICs to possess a dielectric material having a low dielectric constant. Generally, CVD films do not possess low dielectric constants unless they are doped with high levels of fluorine. See Takeshi, S., et al., xe2x80x9cStabilizing Dielectric Constants of Fluorine-Doped-Silicon Dioxide Films by N2O-Plasma Annealing,xe2x80x9d Dielectrics for VLSI/ULSI multilevel Interconnection Conference (DUMIC) (Febuary 1995). However, such fluorine-doped oxides are usually unstable and susceptible to degradation in moist and oxygen plasma environments.
Although a lower dielectric constant may be obtained by using spin-on polymer-containing films (xe2x80x9cSOPsxe2x80x9d), such films pose great challenges for process integration due to their poor thermal stability, their tendency to degrade when exposed to oxygen plasmas, and their tendency to decompose at temperatures typically used for metal layer deposition in ICs. Furthermore, the lowest dielectric constant that can be achieved for SOGs which have been thermally cured is typically only about 3.8-4.1. Such dielectric values may not be suitable for the end uses of the next generation microelectronic applications due to more stringent controls on mechanical and electrical effects such as capacitance that are becoming more critical as device dimensions are reduced.
It would be desirable to provide an improved process for rapidly processing dielectric film coatings on substrates at low temperatures which would result in a product that was thermally stable and insensitive to oxygen plasma. It would also be desirable to provide a uniformly dense SOG or CVD material possessing a low dielectric constant. Moreover, it would be desirable to uniformly grow ultra-thin gate oxides on substrates.
In accordance with this invention, there is provided an improvement in the curing of a dielectric material on a substrate comprising:
(a) applying to a surface of the substrate a dielectric material; and
(b) exposing said dielectric material to electron beam radiation under conditions sufficient to cure the dielectric material.
In accordance with another aspect of this invention, there is provided an improvement in the annealing of a substrate coated with a chemical vapor deposited material comprising:
a) applying to the surface of the substrate the chemical vapor deposited material; and
b) exposing the chemical vapor deposited material to electron beam radiation under conditions sufficient to anneal the chemical vapor deposited material.
In accordance with another aspect of this invention, there is provided an improvement in the growth of ultra-thin film oxides or nitrides on a substrate comprising:
a) exposing a surface of the substrate to electron beam radiation in the presence of a material in a gaseous state and under conditions sufficient to ionize the material and promote an oxidization or nitridation reaction on the surface of the substrate.
In accordance with yet another aspect of this invention, there is provided a substrate coated with an electron beam processed film produced according to the above processes.
In accordance with another aspect of this invention, there is provided a process for reducing the dielectric constant in dielectric film and chemical vapor deposit film coated substrates comprised of exposing said film to electron beam radiation under conditions sufficient to process said film.
In accordance with another aspect of this invention, there is provided a process for producing silicon rich films from chemical vapor deposit coatings comprised of exposing said coatings to electron beam radiation under conditions sufficient to process said film.
In yet another embodiment of this invention, there is provided a microelectronic device containing a substrate coated with an electron-beam processed film, wherein the dielectric constant of said electron-beam processed film is less than about 3.
The electron-beam processed films of this invention not only advantageously form a dense, uniform coating on substrates, but also electron beam cured SOG films possess a dielectric constant which is significantly lower than that reported for similar compositions which were thermally treated at high temperatures. Moreover, the time and temperature for processing such films is significantly reduced.